Fork level indicator for a lift truck

ABSTRACT

A lift truck, including a mast and fork structure movable upwardly and downwardly thereof, includes a level indicating device associated with such mast. The level indicating device includes a casing fixed to the mast, and a cylindrical member pivotally mounted within the casing and having its center of gravity spaced from the pivot axis thereof. Indicating marks associated with the cylindrical member and casing may be viewed by the operator of the lift truck to indicate the relative positions of the cylindrical member and casing, the position of the cylindrical member always being such that the center of gravity thereof lies directly below the pivot axis, so that the levelness of the mast and fork lift structure may be observed.

United States Patent 1191 Wilhelm 1451 May 13,1975

[ FORK LEVEL INDICATOR FOR A LIFT TRUCK [75] Inventor: William G.Wilhelm, 'Painesville,

Ohio

[73] Assignee: Towmotor Corporation, Mentor,

Ohio

[22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,334

[52] US. Cl 214/672; 116/124 R; 33/391;

33/396; 33/370 [51] Int. Cl. 365g 47/00 [58] Field of Search214/670-674,

214/761; 212/39 A; 116/114, 124 R, 124 C, 124 F; 33/365, 391, 396, 370;73/142, 382,

Primary Examiner-Robert .l. Spar Assistant Examiner-R. B. JohnsonAttorney, Agent, or FirmPhillips, Moore, Weissenberger, Lempio &Strabala [57] ABSTRACT A lift truck, including a mast and fork structuremovable upwardly and downwardly thereof, includes a level indicatingdevice associated with such mast. The

431, 482 level indicating device includes a casing fixed to the mast,and a cylindrical member pivotally mounted [56] References Cited withinthe casing and having its center of gravity UNITED STATES TEN spacedfrom the pivot axis thereof. Indicating marks 1,750,962 3/1930Lichtenberg 212/39 A assciatefi with the cylindrical i and 1 1,773,5898/1930 Lichtenberg.... 212/39 A may be V'ewed by the epereter ef the2,033,12-7 3/1936 Dunlea 33/396 x Cate the relative Positions of theCylindrical member 2,374,298 4/1945 212/39 A and casing, the position ofthe cylindrical member a1- 2,677,193 5/1954 ways being such that thecenter of gravity thereof lies 2,877,561 3/l directly below the pivotaxis, so that the levelness of 2,924,022 2/ 1960 the mast and fork liftstructure may be observed. 2,990,622 7/1961 3,243,338 4/1966 4 Claims, 4Drawing Figures PATENTEB MAY 1 3 I95 SHEET 2 OF 2 FORK LEVEL INDICATORFOR A LIFT TRUCK BACKGROUND OF THE INVENTION This invention relates tolevel indicating devices, and more particularly, to such a device forassisting the operator of a lift truck in positioning the lifting forkthereof in a level fore and aft position during operation.

In the use of a lift truck which utilizes forks for lifting andtransporting loads, it is extremely important for the proper efficientuse thereof that such forks be positioned in a substantially levelmanner. Such positioning, for example, is required in order to preventthe tips of the forks from striking pallets, or the products stackedupon such pallets, when attempting to load them on to such forks.Similarly, it is necessary that the load on the forks be disposed in asubstantially level po- 'sition to prevent damage when depositing theload on storage racks or upon other loads. It is also particularlyimportant for the loads to be disposed in a substantially level mannerat extreme lifting heights for safety reasons. However, in relation tothis important point, it is extremely difficult under ordinarycircumstances for an operator of the vehicle to determine if the load isin such a level position, if the forks are at such extreme heights thatthey are substantially above his eye level.

In an. attempt to overcome these problems, several types of levelindicating devices have been previously devised for assisting theoperator in determining the position of his lifting forks. One type oflevel indicator currently being used includes a pair of relativelymovable indicating elements connected between the mast and the body ofthe truck. However, such an indicator is capable of only providing theoperator with the position of the forks relative to the lift truck bymeasuring the angle therebetween, and thus is not capable of indicatinga true horizontal position of the forks. Consequently, deviations due toan irregular or a sloped floor surface or the bending of the forks andmast under the weight of the load are not taken into account by such anindicator. Also such an indicator has been found not to be readilyadaptable to a wide variety of lift trucks, and is relatively expensive.

Another type of level indicator uses various types of gravity sensingelectrolytic potentiometers which are relatively complex and expensive,and have been found to become relatively frequently inoperative, due toa failure in any of many components thereof.

Devices which indicate the position of one element relative to another,similar to the first-described prior art system above, are disclosed inU.S. Pat. No. 2,767,394 to Arnot et al, U.S. Pat. No. 3,017,046 to Runciet al, U.S. Pat. No. 3,049,257 to Bertenshaw et al, U.S. Pat. No.3,077,179 to Evanson, U.S. Pat. No. 3,141,563 to Fisher, and U.S. Pat.No. 3,251,493 to Popelier. Similar to such first-described prior artembodiment, these devices are not capable of indicating a true level orhorizontal condition but are only capable of indicating the position ofone member relative to another.

Of more general interest in this area are U.S. Pat. No. 2,611,188 toBell, and U.S. Pat. No. 3,319,816 to Christenson.

SUMMARY OF THE INVENTION It is an object of this invention to providelevel indicating apparatus which is capable of indicating to theoperator of a lift truck a true substantially horizontally or levelposition of the forks thereof.

It is a further object of this invention to provide level indicatingapparatus which, while fulfilling the above object, may be adapted toany of a wide variety of lift trucks.

It is a still further object of this invention to provide levelindicating apparatus which, while fulfilling the above objects, properlyindicates the levelness of the forks either in a loaded or an unloadedcondition thereof.

It is a still further object of this invention to provide levelindicating apparatus which, fulfilling the above objects, can easily beadjusted for wear in the lifting apparatus, for bent forks of thelifting apparatus, or the like.

It is a still further object of this invention to provide levelindicating apparatus which, while fulfilling the above objects, isextremely simple in construction and convenient for use.

Broadly stated, the invention comprises a level indicating device foruse with a member, such level indicating device comprising a first bodyfixed relative to the member, and a cylindrical body having a center ofgravity spaced from the longitudinal axis of the cylinder. Meanspivotally interconnect the cylindrical body and first body so that thecylindrical body is pivotable relative to the first body about thelongitudinal axis of the cylinder. First indicia means are fixedrelative to the first body, and second indicia means are fixed relativeto the cylindrical body and movable therewith upon pivoting thereof,variations in the levelness of the member which causes pivoting of thecylindrical body relative to the first body being indicated byvariations of the relative positions of the first and second indiciameans.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of theinvention will become apparent from a study of the followingspecification and drawings, in which:

FIG. 1 is a side elevation of a lift truck incorporating the inventivelevel indicating device;

FIG. 2 is a perspective view of the level indicating device of FIG. 1;

FIG. 3 is a front elevation of the level indicating device of FIGS. 1and 2; and

FIG. 4 is an exploded perspective view of the level indicating device asshown in FIGS. 1-3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, alevel indicating device is generally shown at 10 in association with afork-type truck 12. The lift truck 12 includes a lift truck body 14having an operators station provided thereon generally indicated at 16.A substantially upright mast 18 is pivotally attached at its lower endto the body 14 about a pivot axis shown at 20 for tilting movement in afore and aft direction relative to the body 14. One or more tilt jacks22 are pivotally connected between the mast l8 and body 14 to effectsuch fore and aft tilting of the mast 18. A vertically movable liftingplatform 24 is connected to a movable mast member 26 associated with themast 18 and includes a pair of horizontally extending laterally spacedforks 28 suitably connected thereto. The platform 24 and forks 28 makeup load carrying means movable upwardly and downwardly of the mast 18.

As best shown in FIGS. 24, and more particularly in FIG. 4, the levelindicator of the present invention includes a first body 32 or casinghaving a pair of vertically disposed laterally spaced sidewalls 34,36.The peripheries of the sidewalls 34,36 are interconnected by a forwardlydisposed upright mounting wall 38, opposite top and bottom walls 40,42,respectively, and an arcuately shaped face wall 44. The face wall 44defines an opening 46 which is closed by a magnifying lens 48. Acentrally disposed inwardly projecting cylindrical sleeve 50 is formedon the sidewall 36, and the opposite sidewall 34 is provided with acircular opening 52 which is normally closed by a circular cover plate54. The cover plate 54 includes a transversely disposed shaft 56extending inwardly therefrom, having an enlarged cylindrically shapedboss 58 formed on its end adjacent to the cover plate 54. In the instantembodiment, the shaft 56 and the boss 58 are formed integrally with thecover plate 54 and are of the same material, i.e., for example, nylon.The opposite end of the shaft 56 is received within and mounted by thesleeve 50 which is coaxially aligned therewith.

The casing 32, made up of sidewalls 34,36, wall 38, top and bottom walls40,42, face wall 44, magnifying lens 48, and cover plate 54, defines achamber 60. A cylindrical body-62 is disposed within the chamber 60(FIG. 4). Such cylindrical body 62 defines a bore 64 formed therethroughalong the longitudinal cylindrical axis 66 thereof. A sleeve bearing 68is secured within the bore 64 for pivotally or rotatably mounting thecylindrical body 62 on the shaft 56. The cylindrical body 62 ispivotable relative to the casing about the longitudinal axis 66 of thecylinder. The opposite ends of the sleeve bearing 68 are disposedadjacent the inward ends of the sleeve 50 and the boss 58, respectively,to limit the axial movement of the cylindrical body 62 on the shaft 56.

The cylindrical body 62 includes a first body portion 70 which definesthe cylindrical outer surface of the cylindrical body 62, and is ofmaterial of relatively low density, such as plastic. The cylindricalbody portion 70 defines a bore 72 spaced from the longitudinal axis 66of the cylinder as shown, and in which is disposed a second body portion74 of relatively high density material, such as lead. It will be seenthat, by the above construction, the center of gravity of thecylindrical body 62 is spaced from or offset from the longitudinal axis66 of the cylinder defined by such cylindrical body 62, and the body 62will adopt a position on shaft 56, under the force of gravity, with thecenter of gravity thereof substantially directly below the longitudinalaxis 66 of the cylinder.

A segment of colored tape 76, i.e., indicia means, having a horizontaltransversely disposed bisecting line 78 formed thereacross, is affixedto the cylindrical surface of the cylindrical body 62. The magnifyinglens 48 permits clear viewing of the line 78 across the tape 76. A pairof strips of tape 80,82 (i.e., indicia means), are affixed to theoutside of the face wall 44 on opposite sides of the lens 48. The stripsof tape 80,82 are individually provided with horizontally disposed lines84,86 respectively, extending thereacross.

A threaded aperture 88 which is normally closed by a plug 90 is formedin the top wall 40 to permit the filling of the chamber 60 with viscousfluid, such as glycerine, for damping oscillatory movement of thecylindrical body 62 during operation of the device 10.

In the use of the device 10, the casing 32 is attached to the mast 18,such casing 32 being positioned so that the longitudinal axis 66 of thecylinder of cylindrical body 62 is substantially parallel to the pivotaxis 20 of the mast 18. The device 10 should be attached to such mast 18so as to be located as near as possible to the vehicle operators eyelevel. The casing 32 is attached to a substantially vertical surface ofthe mast 18 by cementing the mounting wall 38 thereto with any suitableadhesive. Once the casing 32 is so secured to the mast 18, the device10, is calibrated by raising the lifting forks 28 to their maximumheight and accurately leveling them by the use of a carpenters level orother device. With the forks 28 in such a level empty position, theindicating device 10 is calibrated by affixing the strip of tape 80 onthe left hand side of the lens 48 under an E or empty designation formedon face wall 44, so that its line 84 is aligned with the line 78 on thetape 76 on cylindrical body 62. The level indicating device 10 is nowset to indicate the level or tilt of the forks 28 in their unloadedstate.

The above procedure is repeated with the forks 28 handling the heaviestloads that are to be handled, and raised to their maximum height. Whenthe load is in a level position, the strip of tape 82 is affixed on theright side of the lens 48 under an L or loaded designation so that itsline 86 is aligned with the cylindrical body line 78. The levelindicating device 10 is thereby set to indicate the level position ordirection of tilt when the forks 28 are loaded. It will be seen that, bynoting variations of the relative positions of the indicia means, thelevelness of the mast l8 and load carrying means due to the pivoting ofthe mast 18 about the pivot axis 20 thereof, or due to any othermovement of the mast 18 relative to a level position thereof, may benoted.

The elevational difference between lines 78,86 automatically compensatesfor the bending of the forks 28 and the mast 18 under the load, so thatthe operator can readily determine if the forks 28 are level in both theloaded and empty conditions. Red and green areas on the tape 76 aboveand below the line 78 thereon may be included, and may with advantage beindicated with aluminum paint, in order that the tape 76 may be clearlyvisible when the vehicle 12 is being operated in a dimly lit area.

The red or warning indication on the level indicating device 10 will beseen when the forks 28 are tilted forwardly to denote the possibility ofthe load shifting the center of gravity of the vehicle ahead of thefront axle, resulting in the danger of tipping or the load sliding offthe forks 24. Conversely, the green or safe indication on the levelindicating device 10 will be noted when the forks 28 are tiltedrearwardly, which denotes that the load is being safely carried.

The device disclosed herein, it will be seen, may be adapted to thestationary mast of any lift truck for assisting the operator of suchlift truck in positioning the lifting forks thereof in a level position.The device is extremely simple, and will perform properly for anextremely great period of time. The viscous fluid used in the chamber 60acts to dampen the oscillation of the cylindrical body 62 in itsoperation, and provide an accurate reading with minimum time delay.

The level indicating device can be periodically checked for accuracy andadjusted, if necessary, to compensate for wear in the mast assembly,lifting platform, or for bent forks, by simply replacing or adjustingthe strips of tape 80, 82 on either side of the magnifying lens 48.

What is claimed is: 1. In combination with a vehicle having a mastpivotable relative to the vehicle about a pivot axis, means to pivotsaid mast, load carrying means movable upwardly and downwardly on saidmast and a device for indicating the levelness of said mast and loadcarrying means in a plurality of load carrying conditions comprising:

a first body fixed on said mast; a cylindrical body having its center ofgravity spaced from the longitudinal axis of said cylindrical body;

means pivotally interconnecting the cylindrical body and first body sothat the cylindrical body is pivot,- able relative to the first bodyabout the longitudinal axis of said cylindrical body, the cylindricalbody being further positioned so that said longitudinal axis of thecylinder is substantially parallel to the pivot axis of the mast;

first and second indicia means fixed relative to the first body toindicate the levelness of said mast and load carrying means when theyare in a first and second load carrying condition, respectively; and

third indicia means fixed relative to the cylindrical body and movabletherewith upon pivoting thereof, variations in the levelness of the mastand load carrying means due to pivoting of the mast about the pivot axisthereof being indicated by variations of the relative position of thefirst and second indicia means relative to said third indicia means.

2. The device of claim 1 wherein the cylindrical body comprises a firstportion defining the cylindrical outer surface of the cylindrical body,and a second portion of density greater than the first portion, thefirst portion defining a bore spaced from the longitudinal axis of saidcylindrical body, and in which is disposed the second portion.

3. The device of claim 2 wherein the first body comprises a casingdefining a chamber within which the cylindrical body is disposed, andfurther comprising viscous fluid substantially filling the remainder ofthe chamber.

4. The device of claim 3 wherein the second indicia means are fixed tothe cylindrical outer surface of the cylindrical body, and wherein thecasing further comprises window means through which the second indiciameans may be viewed.

* II! I

1. In combination with a vehicle having a mast pivotable relative to thevehicle about a pivot axis, means to pivot said mast, load carryingmeans movable upwardly and downwardly on said mast and a device forindicating the levelness of said mast and load carrying means in aplurality of load carrying conditions cOmprising: a first body fixed onsaid mast; a cylindrical body having its center of gravity spaced fromthe longitudinal axis of said cylindrical body; means pivotallyinterconnecting the cylindrical body and first body so that thecylindrical body is pivotable relative to the first body about thelongitudinal axis of said cylindrical body, the cylindrical body beingfurther positioned so that said longitudinal axis of the cylinder issubstantially parallel to the pivot axis of the mast; first and secondindicia means fixed relative to the first body to indicate the levelnessof said mast and load carrying means when they are in a first and secondload carrying condition, respectively; and third indicia means fixedrelative to the cylindrical body and movable therewith upon pivotingthereof, variations in the levelness of the mast and load carrying meansdue to pivoting of the mast about the pivot axis thereof being indicatedby variations of the relative position of the first and second indiciameans relative to said third indicia means.
 2. The device of claim 1wherein the cylindrical body comprises a first portion defining thecylindrical outer surface of the cylindrical body, and a second portionof density greater than the first portion, the first portion defining abore spaced from the longitudinal axis of said cylindrical body, and inwhich is disposed the second portion.
 3. The device of claim 2 whereinthe first body comprises a casing defining a chamber within which thecylindrical body is disposed, and further comprising viscous fluidsubstantially filling the remainder of the chamber.
 4. The device ofclaim 3 wherein the second indicia means are fixed to the cylindricalouter surface of the cylindrical body, and wherein the casing furthercomprises window means through which the second indicia means may beviewed.